Long-term investigation of microbial fuel cells treating primary sludge or digested sludge

The long-term performance of sludge treatment in microbial fuel cells (MFCs) was examined by operating two MFCs for almost 500 days. In Phase I, one MFC fed with primary sludge removed 69.8 ± 24.1% of total chemical oxygen demand (TCOD) and 68.4 ± 17.9% of volatile suspended solids (VSS); the other MFC with digested sludge reduced 36.2 ± 24.4% of TCOD and 46.1 ± 19.2% of VSS. In Phase II, both MFCs were operated as a two-stage system that removed 60% of TCOD and 70% of VSS from the primary sludge. An energy analysis revealed that, although the total energy in the MFC system was comparable with that of anaerobic digesters, the electric energy had a minor contribution and methane gas still dominated the total energy production. The results suggest that MFCs may not be suitable for treating primary sludge for energy recovery, but could potentially be used to polish the effluent from anaerobic digesters.